18.20 Controlling Alien (Invasive) Species

Definition of Alien Species

• Alien Species (Invasive Species): Species that are introduced, either intentionally or unintentionally, to a new ecosystem where they were previously unknown.
• These species can disrupt native ecosystems, outcompete local species, and often lack natural predators in their new habitats.

Causes of Alien Species Introduction

• Human Activity:
  • Trade and Transport: Plants, animals, and even seeds or larvae can be carried accidentally on ships, planes, or vehicles.
  • Intentional Introductions: Some species are introduced to control pests or as ornamental plants but can become invasive.
  • Accidental Escapes: Species sometimes escape from captivity or cultivation, such as pets or garden plants spreading into wild ecosystems.

Examples of Invasive Species and Their Impacts

1. Small Indian Mongoose (Herpestes auropunctatus)

• Origin: India
• Introduction: Introduced to Jamaica in 1872 to control rat populations in sugarcane fields.
• Negative Impact: Became a predator of native animals, threatening local wildlife instead of solely targeting rats.

2. Cane Toad (Rhinella marina)

• Origin: South America
• Introduction: Brought to Queensland, Australia, from Hawaii in 1935 to control beetles harming sugarcane.
• Negative Impacts:
  • Rapid Reproduction: The toad population exploded, spreading across large parts of Australia.
  • Toxin Production: Cane toads produce a strong toxin that kills most animals that try to eat them.
  • Predatory Impact: Threatens the endangered northern quoll (Dasyurus hallucatus), which often tries to eat the toxic toads.
  • Competition with Native Species: Likely competes with native amphibians for food and eats the chicks of native ground-nesting birds, such as the rainbow bee-eater (Merops ornatus).

3. Red Lionfish (Pterois volitans)

• Origin: South East Asia
• Introduction: Likely escaped from aquariums in the United States and spread throughout the Caribbean.
• Negative Impacts:
  • Coral Reef Threat: Consumes native fish species on coral reefs, reducing biodiversity.
  • No Natural Predators: Has no significant predators in the Caribbean, allowing it to grow unchecked.
• Control Efforts:
  • In Belize, divers are encouraged to spear lionfish to control their population.
  • Jamaican government promotes the fish as a delicacy to encourage fishing for lionfish.

4. Water Hyacinth (Eichhornia crassipes)

• Origin: South America
• Introduction: Spread to various tropical and subtropical regions.
• Negative Impacts:
  • Aquatic Ecosystem Disruption: Forms dense mats on water surfaces, blocking sunlight and reducing oxygen levels, which can kill native aquatic plants and fish.
  • Human Health Risk: Provides a breeding ground for mosquito larvae, increasing malaria and other mosquito-borne diseases.
• Control Importance: Controlling water hyacinth is critical to protect aquatic ecosystems and human health.

5. Japanese Knotweed (Fallopia japonica)

• Origin: Japan
• Introduction: Originally brought to Europe and North America as an ornamental plant.
• Negative Impacts:
  • Structural Damage: Its strong root system can damage buildings, roads, and walls.
  • Outcompetes Native Plants: Grows aggressively, reducing space for native species, leading to decreased plant diversity.

Impacts of Alien Species on Ecosystems

1. Predation:

• Some invasive species become predators of native species, especially if native prey lack defenses against them.
• Example: Small Indian mongoose in Jamaica, preying on native animals.

1. Competition:

• Invasive species can outcompete native species for resources like food, habitat, and light, often pushing natives to local extinction.
• Example: Japanese knotweed crowds out native plants.

1. Disease Introduction:

• Alien species may introduce pathogens or parasites to which native species have no immunity, leading to disease outbreaks.

1. Ecosystem Alteration:

• Some species, particularly invasive plants, can change the structure and function of ecosystems.
• Example: Water hyacinth decreases oxygen levels in water, harming aquatic life.

1. Habitat Modification:

• Invasive plants may change soil chemistry, light availability, and physical habitat structures, making conditions less suitable for native species.
• Example: Japanese knotweed’s root systems can alter soil structure and prevent other plants from establishing.

Control and Management of Alien Species

• Physical Removal:
  • Manual Removal: In areas where invasive species populations are still small, physical removal can be effective.
  • Example: Spearing lionfish in the Caribbean.
• Biological Control:
  • Introduction of Natural Predators: Carefully selected predators or diseases are introduced to control invasive species.
  • Risks: Must be done cautiously to avoid unintended impacts on native species.
  • Public Engagement and Incentives:
  • Encouraging local populations to help control invasive species by providing economic incentives or raising awareness.
  • Example: Jamaican government encourages people to eat lionfish as a way to reduce its population.
• Chemical Control:
  • Use of Herbicides or Pesticides: Applied in controlled settings to eliminate invasive plants or insects.
  • Risks: Potential environmental impact, including harm to non-target species and ecosystems.
• Habitat Restoration:
  • After invasive species removal, restoring native plants and animals to re-establish ecosystem balance.

Studying the Impact of Alien Species

How to Investigate Alien Species Impact on Ecosystems

1. Set Up Controlled Study Sites:

• Select multiple sites within the ecosystem, some with the invasive species and some without, to observe differences.

1. Measure Biodiversity:

• Record the number and types of native species present in both invaded and non-invaded areas.
• Compare species richness and evenness.

1. Assess Abiotic Factors:

• Record light availability, soil or water quality, oxygen levels, and other abiotic factors that might be impacted by the invasive species.
• Example: Measure oxygen levels in water to assess the impact of water hyacinth on aquatic life.

1. Monitor Long-Term Changes:

• Track changes over time to see if native species decline, invasive species spread, or ecosystem structure changes.
• Record any recovery if invasive species are removed.

1. Investigate Competition and Predation:

• Observe if invasive species are directly preying on or competing with native species for food, habitat, or other resources.

Summary of Key Points

1. Definition of Alien Species: Species introduced to new ecosystems where they were previously unknown.
2. Causes of Introduction: Trade, transport, intentional biological control, accidental escapes.
3. Examples and Impacts:

• Small Indian Mongoose: Predation on native Jamaican species.
• Cane Toad: Toxic predator impacting northern quoll in Australia.
• Red Lionfish: Predation on Caribbean coral reef species.
• Water Hyacinth: Reduces sunlight and oxygen in water bodies, impacting aquatic ecosystems.
• Japanese Knotweed: Outcompetes native plants and damages infrastructure.

1. Control Methods:

• Physical removal, biological control, public engagement, chemical control, and habitat restoration.

1. Investigating Impacts:

• Set up study sites, measure biodiversity and abiotic factors, and monitor changes over time.

Review Questions

1. Explain how alien species damage ecosystems:

• By predation, competition, disease introduction, ecosystem alteration, and habitat modification.

1. Suggest a method for investigating the effect of an invasive plant on biodiversity:

• Set up study sites, measure biodiversity, monitor changes, and compare invaded vs. non-invaded areas.

1. Key Term:

Alien Species: A species introduced to a new ecosystem where it can cause harm due to lack of natural predators or competition.